1. Field of the Invention
The present invention relates to a tool to be attached to a spindle of a machine tool for machining a workpiece.
2. Description of the Related Art
In for example a machining center or other machine tool provided with a spindle, the maximum rotational speed of the spindle is determined by the structure of a main bearing rotatably supporting the spindle and a lubrication system of this bearing. For this reason, when it is necessary to rotate a tool at a higher rotational speed than the maximum rotational speed of the spindle, an accelerating apparatus is used.
As the accelerating apparatus, for example, an accelerating apparatus provided with a gear mechanism such as epicyclic gearing which holds the tool and is removably attachable to the spindle is well known.
For example, in a machining center, when it is desired to increase the rotational speed of the tool to higher than the maximum speed of the spindle temporarily, an accelerating apparatus such as the above accelerating apparatus is attached to the spindle in the same way as an ordinary tool to enable the tool to be rotated at a higher rotational speed.
However, when raising the rotational speed of the tool to a higher speed than the maximum rotational speed of the spindle by the above gear mechanism, the accelerating apparatus increasingly generates heat at a super high rotational speed such as tens of thousands to hundreds of thousands of revolutions per minute, so the machining tolerance of a workpiece can be influenced by the heat. Further, at the above super high rotational speed, the noise from the accelerating apparatus can also increase. Furthermore, a highly reliable precision structure able to withstand the above super high rotational speed is required for the accelerating apparatus, so there is the disadvantage that the manufacturing cost becomes relatively high.
Further, in a case of an accelerating apparatus with a gear mechanism, it is needed to lubricate the gear or bearing and arrange a supply passage and a discharge passage for the lubricating oil in the accelerating apparatus, so there is the disadvantage that the apparatus becomes larger and it is difficult to automatically change the tool by an automatic tool changer.
An object of the present invention is to provide a tool and a tool holder to be removably attached to a spindle of a machine tool in the same way as an ordinary tool, capable of operating without connecting an external power supply etc., giving a higher rotational speed than that of the spindle of the machine tool, and automatically changing a tool.
Another object of the present invention is to provide a machine tool provided with the above tool and tool holder.
According to a first aspect of the present invention, there is provided a tool attachable to a spindle of a machine tool comprising a machining tool for machining a workpiece; a motor for driving the machining tool; a generator for generating electric power to drive the motor by the rotation of the spindle; and a breaking means for breaking a supply line of electric current from the generator to the motor when electric current over a predetermined value flows in the supply line.
According to a second aspect of the present invention, there is provided a tool attachable to a spindle of a machine tool comprising a machining tool for machining a workpiece; a motor for driving the machining tool; a generator for generating electric power to drive the motor by the rotation of the spindle; a control means for controlling a supply of electric power generated by the generator to drive and control the machining tool; and a driving state detecting means for detecting the state of the motor; wherein the control means drives and controls the motor based on the information detected by the driving state means.
According to a third aspect of the present invention, there is provided a tool attachable to a spindle of a machine tool comprising a machining tool for machining a workpiece; a motor for driving the machining tool; a generator for generating electric power to drive the motor by the rotation of the spindle; a light signal generation means for generating light signal in accordance with the rotational speed of the motor; and a light guiding means for guiding light into the light signal generation means from outside to output the light signal by the light signal generation means to the outside.
According to a fourth aspect of the present invention, there is provided a tool attachable to a spindle of a machine tool comprising a machining tool for machining a workpiece; a motor for driving the machining tool; a generator for generating electric power to drive the motor by the rotation of the spindle; a rotational speed detecting means for detecting the rotational speed of the motor; and a rotational speed displaying means for displaying the rotational speed detected by the rotational speed detecting means so as to be visually recognized from the outside.
In the first aspect of the present invention, the tool attachable to the spindle is provided with a generator and a motor, generates electric power using the rotation of the spindle, drives the motor with the generated electric power, and rotates the cutting tool. By this, it becomes possible to drive the tool without connecting with the external power supply, etc. and also change automatically the tool.
Further, the tool of the present invention generates electric power using the rotation of the spindle. Due to this, even when the cutting tool is overloaded while machining, the spindle is driven continuously. So, there is a possibility that the excessive current flows in the generator or the
Accordingly, in the present invention, if the current over predetermined value flows the supply line from the generator to the motor, the generator and the motor are protected by breaking the supply line.
In the second aspect of the present invention, the driving state of the motor is detected by the driving state detecting means and is fed back to the control means to control the motor. By this, it becomes possible to control the tool independently of the spindle, variously and precisely.
In the third aspect of the present invention, the tool is provided with a light signal generating means and a light guiding means and generates light signal in response to the rotational speed of the motor by the light generating means using light input from outside, and outputs the light signal to outside. By detecting the rotational speed of the motor based on the output light signal, a light source or a light receiving device is not necessarily built in the tool and it becomes possible to make the tool compact.
In the fourth aspect of the present invention, the tool attached to the spindle is provided with a generator and a motor, generates electric power by the rotation of the spindle, and drives the motor with the generated electric power to rotate the cutting tool. When the motor rotates, the rotational speed is detected by the rotational speed detecting means and is displayed visually recognizably by the rotational speed display means. Due to this, it is possible to grasp easily the driving state of the tool.